Slow wave structure for use in a magnetron



Feb. 18, 1964 SE PUAN YU 3,

SLOW WAVE STRUCTURE FOR USE IN A MAGNETRON Filed Oct. 5. 1960 2 Sheets-Sheet 1 F|G.|.

INVENTOR: SE PUAN YU SE PUAN YU SLOW WAVE STRUCTURE FOR USE IN A MAGNETRON Feb. 18, 1964 2 Sheets-Sheet 2 Filed Oct. 5, 1960 IN VE NTOR SE PUAN Yu,

HIS ATTORNEY.

United States Patent 3,121,821 SLGW WAVE STRUTURE FQR UE EN A MAGNE'ERQN e Penn Yu, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Get. 5, i966, Ser. No. 60,739 17 Claims. ('Cl. 315-3969) This invention relates to slow wave structures and more particularly to a new and improved slow wave structure for use in a magnetron and adapted for preventing the magnetron from operating in a spurious mode or at an undesired frequency.

The conventional magnetron oscillator has an anode comprising a re-entrant series of coupled resonant cavities. Such a resonant slow wave structure has a number of fundamental resonant modes equal to one-half the number of resonant cavities plus one. Besides these fundamental modes, there are high-order bandpasses and each bandpass has spatial harmonics. Therefore, the conventional magnetron anode has an infinite number of resonant modes. When the magnetron is operated as a pulsed oscillator, a regenerative growth of high frequency energy is possible in many of the mode points through hich the voltage sweeps during the rise and decay of the pulse. Further, any temporary lack of emission can cause the device to lock-in on a spurious mode having a synchronous phase velocity corresponding to the desired voltage during the pulse. This operation in spurious modes has previously placed an upper limit on the maximum power output and life of the pulsed magnetron oscillator.

It is, accordingly, an object of this invention to provide a magnetron which will assuredly operate at the predetermined mode and frequency for which it was designed to operate.

It is a further object of this invention to provide a slow wave structure which will support an electromagnetic wave of only a predetermined frequency.

:It is a further object of this invention to provide a slow wave structure which presents a uniform impedance to an electromagnetic wave of a design mode and frequency which presents a nonuniform impedance to oth r electromagnetic waves.

It is a further object of this invention to provide a magnetron in which all longitudinal modes of operation are eliminated.

Briefly stated, in accordance with one aspect of this invention, an anode block for a cavity resonator is provided in which the resonant cavities are of different sizes. Cooperating with the cavities are strapping rings including sections which are predetermineclly dimensioned such that the impedance presented by each cavity and the respective sections t the strapping rings associated therewith is uniform for the design mode and frequency but is not uniform for any other mode or frequency.

in copending Donald A. Wilbur application Serial No. 65,716, filed Oct. 28, 1960, entitled Mixed Lines Crossed Fields Oscillator or Amplifier and assigned to the assignee of the present application, there is disclosed and broadly claimed apparatus embodying a slow wave structure having two or more portions with frequency versus phase shift per section characteristics which intersect for only one frequency. The invention of the said Wilbur application was made prior to my invention and, therefore, I make no claim to the broad invention of the said Wilbur application and I claim herein only an improvement, of the broad invention, embodying strapping means having sections of dilferent sizes.

For a better understanding of the invention, reference may be had to the accompanying drawings in which:

FIG. 1 shows a plan View of a magnetron anode block embodying certain aspects of the invention;

FIG. 2 shows developed views of the strapping rings to be used with the embodiment shown in FIG. 1;

FIGS. 3 and 4 show the strapping rings of PEG. 2 attached to the anode block of PEG. 1;

FIG. 5 shows a partially sectionalized View of an anode block utilizing the embodiment of the invention shown in FIG. 1;

PEG. 6 shows a plan View of a magnetron anode block including strapping rings using another embodiment of the invention; and,

FIG. 7 shows developed views of the strapping rings shown in FIG. 6.

In FIG. 1 is shown an anode block it employing one embodiment of the invention which may be used in any cavity resonator magnetron. The anode block 1 is adapted for encircling and cooperating with a concentric cathode 9 and includes ten segments or vanes 11 through 2% which form ten resonant cavities 21 through fill in the lock 1. Of course, the use of ten cavities is merely a matter of design choice, and any desired number of such cavities may be used.

As shown in FIG. 1, the cavities 21 through 3a are of three diiierent sizes, with cavities 21 and 26 being of a first size, cavities 22, 2d, 28 and 29 being of a second size and cavities 23, 25, 27 and 3% being of a third size.

As will be seen from the following, the number of difierent sizes which the cavities can take need not be limited to three, but may be any number greater than one, up to and including the total number of cavities used.

FIG. 2 shows developed views of strapping rings 2, 3, 4- and 5 to be used with the anode clock It and FIGS. 3, 4 and 5 show the strapping rings 2, 3, 4 and attached to the anode block 1. The strapping ring 2 is conductively attached, as by brazing, to segments 12, i4, 16, 18 and 2d at points 12', 14, 16, 1.8 and 2%, respectively, of ring 2; and ring 3 is in a like manner connected to segments 11, 13, 15', 1'7 and 1.9 at points it, 13', 15, 17' and 19', respectively. in a like manner, strapping rings 4 and 5 are conductively connected to the corresponding segments at their correspondingly numbered positions. As shown in FIGS. 4 and 5, each of the segments 11 through 2.4 has a slot 6 on one side thereof and a slot 7 on the opposite side thereof. The electrical connections between the strapping rings 2 and 3 and the segments 11 through 29 are made in the slot 6 and the electrical connections between the strapping rings 4 and 5 and the segments 11 through 26 are made in the slot 7.

of the strapping rings 2, 3, a and 5 includes sections 21' through fall which pass through and cooperate with cavities 21 through 39, respectively. The dimensions or cross sections of the sections 21' through 3% are varied so that each cavity the sections of the strapping rings 2, f), 4 and 5 cooperating therewith pre sent a uniform impedance at the design mode and frequency. To any other mode and frequency, each (litterent-sized cavity and the sections of strapping rings 2, 3, 4 and 5 cooperating therewith will present a diiierent impedance. Thus, the anode block 1 with the resonant cavities 21 through 34) and the strapping rings 2, 3, -l and 5 terms a slow wave structure 8 which presents a uniform impedance to the design and frequency of operation of a magnetron employing such a slow wave structure. Also, since the slow wave structure 8 presents a uniform impedance to the design frequency, it will support an electromagnetic wave of this predetermined frequency.

The dimensions of the various sized cavities and the sections of strapping rings cooperating therewith may be related according to the equation:

n+yr+ys where y zthe admittance of the interaction space of the mag- HCHOH y =the admittance of the cavity y the admittance of the strapping ring These admittances may be defined by the following equations:

2 fio/ ug l Goth d 1) 6 GS yszjyo 21m cos T sin Isl-cos kl sin kl where P=n+mN m=0, i1, i2, i3, N :number of cavities /e t admittance of free space k w/c w=angular frequency at which the device is to be operated c velocity of light in free space In a magnetron employing the invention as shown thus far, the following dimensions have been found to be satisfactory, for example, for an operating frequency of 2800 megacycles per second:

The depth D of cavities 21 and 26 may be 0.441 inch. The depth of cavities 22, 24-, 28 and 2% may be 0.401 inch. The depth of cavities 23, 25, 2.7 and 30 may be 0.471 inch. The thickness T of each of the strapping rings 2, 3, 4 and 5 may be 0.040 inch. The inner radius R of the inner strapping rings 3 and 4 may be 0.693 inch. The inner radius R of the outer strapping rings 2 and 5 may be 0.803 inch.

With reference now to FIG. 2, the height of the different sections of strapping ring 2 may be as follows: dimension A, the height of the section associated with cavity 21 may be 0.073 inch; dimension B, the height of the section associated with cavity 22 may be 0.105 inch; dimension C, the height of the section associated with cavity 23 may be 0.032 inch; dimension S, the height of the strapping ring 2 at 16', which is attached to anode block 1 between cavities 25 and 26, may be 0.160 inch. The dimensions of the remaining corresponding sections of the strapping ring 2 and also of strapping rings 3, 4 and 5 may be the same as those previously given dimensions A, B, C and S.

In the embodiment above-described, four conductive strapping rings are used, with a first pair of concentric strapping rings alternately contacting adjacent segments on one side of the anode block and a second pair of concentric conductive strapping rings alternately contacting adjacent segments on the opposite side of the anode block. If it is desired, only two strapping rings may be used. When only two strapping rings are used, they may be positioned either both on the same side of the anode block or, preferably, one on each side of the anode block. In both instances, the strappings rings will alternately contact adjacent ones of the segments which divide the anode block into a plurality of resonant cavities.

In the embodiment described, the resonant cavities have been equally spaced from each other and the different sized cavities have been randomly disposed around the anode block. According to the invention, the differentsized cavities may be disposed in any desired manner. If desired, the different-sized cavities may form an ordered patter such as a symmetrical geometric pattern.

In FIG. 6 is shown an embodiment of the invention in which an anode block 1 has an even number of different-sized resonant cavities including a cavity 4-1 which is smaller than any of the other cavities and a cavity 42 positioned diametrically opposite cavity 41 and which is larger than any of the other cavities. The remaining cavities are disposed around the anode block 1 equally spaced from each other and becoming progressively larger from cavity 41 to cavity 42. Strapping rings 43 and 44 alternately connect the adjacent segments which separate the adjacent cavities. Strapping rings 45 and 45, shown in FIG. 7, alternately connect the adjacent segments on the other side of the anode block 1. Again, the dimensions of the sections of the strapping rings cooperating with each cavity are such that each cavity, together with its cooperating sections of strapping rings 43, 44, 45 and 46, presents a uniform impedance when the magnetron employing the invention operates at its design mode frequency.

FIG. 7 shows developed views of the strapping rings 43, 44, 45 and 45 suitable for use with the embodiment shown in FIG. 6. Of course, this embodiment could also use only two strapping rings, as previously described.

While only an anode block and cathode have been shown and described, it is understood that they are to be used in conjunction with other elemnts which would usually be employed in a magnetron; such, for example, as a suitable envelope, power input and output means, a cathode heater, and electrical connections to the heater.

While the abovedescribed embodiments are illustrative of the application of the principles of this invention, it is understood that the invention is not limited thereto. Specifically, the invention is not limited to any particular type of resonator structure but is equally applicable to resonant circuits employing vanes, slots or bores. Additionally, the invention is not limited to the number of resonant cavities shown or to the particular geometric arrangement of the cavities shown. Numerous other embodiments may be devised by those skilled in the art without departing from the spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A slow wave structure comprising a plurality of resonant cavities, said cavities being of a plurality of different sizes and extending in a single plane, a plurality of segments, one each of said segments separating adjacent ones of said cavities, and strapping means connecting alternate ones of said segments, said strapping means being comprised of a plurality of different-sized sections, each one of said different-sized sections cooperating with one of said different-sized cavities to provide a slow wave structure having a uniform impedance for a predetermined irequency and which will support electromagnetic waves of said predetermined frequency.

2. -In a cavity resonator magnetron, an anode block having a plurality of different-sized resonant cavities extending in a common plane therein, a plurality of segments, one each of said segments separating adjacent ones of said cavities, and strapping means connecting alternate ones of said segments, said strapping means being comprised of an annulus having a plurality of dhlerentsized sections, said diilerenesized sections each being predeterminedly dimensioned relative to an associated one of said difierent-sized resonant cavities and cooperating therewith to provide a slow wave structure having a uniform impedance for a predetermined mode and frequency of operation of the magnetron.

3. A slow Wave structure comprising a plurality of resonant cavities, said cavities being or" at least three different sizes, a plurality of segments, on each of said segments separating adjacent ones of said cavities, and strapping means connecting alternate ones of said segments, said strapping means having sections of clirering cross-sect-ioual dimensions to cooperate therewith to provide a slow wave structure having a uniform impedance for a predetermined frequency and which will support electromagnetic waves of said predetermined frequency.

4. In a cavity resonator magnetron, an anode block having a plurality of resonant cavities therein, said cavities being of at least three different sizes, a plurality of segments, one each of said segments separating adjacent ones of said cavities, and strapping means connecting alternate ones of said segments, said strapping means havsections of different dimensions to cooperate therewith to provide a slow wave structure having a uniform impedance for a predetermined mode and frequency of operation of the magnetron.

5. in a cavity resonator magnetron, an anode block having a plurality of resonant cavities in said block, said cavities being of at least three different sizes, a plurality of segments, one each of said segments separating adjacent ones of said cavities, and strapping means comprising at least two circular conductive members, said members alternately contacting adjacent ones of said segirents, each of said morn ers having a plurality of sections each cooperating with respective di cred: individual ones of said cavities, said sections being of at least three different sizes whereby each one of said cavities and the sections of said members cooperating therewith present a substantially uniform impedance to an electromagnetic wave of a predetermined frequency.

6. in a cavity resonator magnetron, an anode block having a plurality of resonant cavities therein, said cavities being of at least three different sizes, a plurality of segments, one each of said segments separating adjacent ones of said cavities, said cavities of different sizes being randomly disposed in said block, and strapping means connecting alternate ones of said segments, said strapping means having difierent size sections dimensior d to co operate therewith to provide a slow wave struc ..re hava uniform impedance for a predetermined mode or" peration of the magnetron.

7. in a cavity resonator magnetron, circular anode block having a plurality of resonant cavities being equally s aced from each other in said block, said cavities being of at least three dir'erent sizes, a plurality of segments, one each of said segments separating adjacent ones of said cavities, said cavities of dillerent sizes being randomly disposed in said block, and strappin means comprising at east two annular conductive members, said members alternately contacting adjacent ones of said segments, each of said members having a plurality of sections cooperating with respective diilerent individual ones of said cavities, said sections being of at least three different sizes whereby each one of said cavities and the sections of said members cooperating there-with present a substantially uniform impedance to an electromagnetic wave of a predetermined frequency.

8. in a cavity resonator, a circular anode block having a plurality of resonant cavities being equally spaced from each other in said block, said cavities being of at least three dillerent sizes, a plurality of segments each having a first end and a second end, one each of said segments separating adjacent ones of said cavities, said cavities of different sizes being randomly disposed in said block, and strapping means comprising two pairs of concentric conductive rings, the first pair of said rings alternately contacting the first ends of the adjacent ones of said segments, the second pair of said rings alternately contacting the second ends of the adjacent ones of said segments, each of s rings having a plurality of sections each cooperating with respective different individual ones of said cavities, said sections being of at least three different sizes whereby each one of said cavities and the sections of said rings cooperating therewith present a substantially uniform impedance to an electromagnetic wave of a predetermined frequency.

9. In a cavity resonator magnetron, anode block having a plurality of resonant cavi ies therein, said cavities being of at least three different sizes, a plurality of segments, one each or" said segments separating adjacent ones of said cavities, said cavities of different sizes being disposed in a symmetrical geometric pattern in said block, and strapping means connecting alternate ones or" said segments, said strapping means having different size sections dimensioned to cooperate therewith to provide a slow iv ve structure having a uniform impedance for a predetermined mode of operation of the magnetron.

10. in a cavity resonator magnetron, a circular anode block having a plurality of resonant cavities being equally spaced from each other in said block, said cavities being of at least three dillerent sizes, a plurality or" segments, one each or said segments separating adjacent ones of said cavities, said cavities of dilterent sizes being disposed in a symmetrical geometric pattern in said block, and stra t means comprising at least two annular conductive members, said members alternately contacting adjacent ones of said segi ents, each of said members having a plrrality of sections each cooperating wi t respective dilterent individual ones of said cavities, said sections being of at least three different sizes whereby each one of said cavities and the sections of said members cooperating therewith present a substantially uniform impedance to an el ctro ag'netic Wave of a predetermined frequency.

11. In a cavity resonator, a circular anode blocs ha ing a plurality of resonant cavities being equally spaced from each other in said block, said cavities being of at least three different sizes, a plurality of segments each having a first end and a second end, one each of said segments sepmating adjacent ones of said cavities, said cavities of different sizes being disposed in a symmetrical geometric pattern in said block, and strapping means comprising two pairs of concentric conductive rings, the first pair of said rings alternately contacting the first ends of the adjacent ones of said segments, the second pair of said rings alternately contacting the second ends of the adjacent ones of said segments, each of said rings having a plurality of sections each cooperating with respective diilerent individual ones of said cavities, said sections being or" at least three diilerent sizes whereby each one of said cavities and the sections of said rings cooperating therewith present a substantially uniform impedance to an electromagnetic wave or" a predetermined frequency.

12. in a cavity resonator magnetron, a circular anode block having an even number of resonant cavitie equally spaced from each other around said block, and an equal even number of segments, one each of said segments separating adjacent ones of said cavities, a first cavity being smaller than any one of the other of said cavities, a second cavity being larger than any one of the other of said cavities, said second cavity being diametrically opposed to said first cavity, the remaining ones of said cavities becoming progressively larger from said first cavity to said second cavity, and strapping means connecting alternate ones of said segments, said strapping means being cross sectionally dimensioned to cooperate therewith to provide a slow Wave structure having a uniform impedance for only a predetermined mode of operation of the magnetron.

13. In a cavity resonator magnetron, a circular anode block having an even number of resonant cavities equally spaced from each other around said block, an equal even number of segments, each one of said segments separating adjacent ones of said cavities, a first cavity being smaller than any one of the other of said cavities, a second cavity being larger than any one of the other of said cavities, said second cavity being diametrically opposed to said first cavity, the remaining ones of said cavities becoming progressively larger from said first cavity to said second cavity, and strapping means comprising at least two annular conductive members, said members alternately contacting adjacent ones of said segments, each of said members having a plurality of sections each coperating with respective different individual ones of said cavities, said sections being of progressively different sizes whereby each one of said cavities and the sections of said memucrs cooperatng therewith present a substantially uniform impedance to an electromagnetic wave of a predetermined frequency.

14. In a cavity resonator magnetron, a circular anode block having an even number of resonant cavities equally spaced from each other around said block, an equal even number of segments each having a first end and a second end, one each of said segments separating adjacent ones of said cavities, a first cavity being smaller than any one of the other of said cavities, a second cavity being larger than any one of the other of said cavities, said second cav ity being diametrically opposed to said first cavity, the remaining ones of said cavities becoming progressively larger from said first cavity to said second cavity, and strapping means comprising two pairs of concentric conductive rings, the first pair of said rings alternately contacting the first ends of the adjacent ones of said segments, the second pair of said rings alternately contacting the second ends of the adjacent ones of said segments, each of said rings having a plurality of sections each cooperating with respective different individual ones of said cavities, said sections being of progressively diiferent sizes whereby each one of said cavities and the sections of said rings cooperating therewith present a substantially uniform impedance an electromagnetic wave of a predetermined frequency.

15. A cavity resonator magnetron anode block as described in claim 8 in which the dimensions of said resonant cavities and said strapping rings are related according to the equation:

y =the admittance of the strapping ring said admittances being defined by the following equations:

yn zjv ta/1 0% y 00th dd cos Zkl-cos N 21521170 211% cos sin ]eZcos kl sin kl wzangular frequency at which the device is to be operated c velccity of light in free space Y =equivalent characteristic admittance of each pair of conductive strapping members as a two wire transmission line l=average length of strap per cavity r =radius of the anode r =radius of the cathode fizangle at which walls of cavity would intersect a distancc from point where walls of cavity would intcrsect to front of cavity b=distance from point where walls of cavity would intersect to back of cavity 16. A cavity resonator magnetron anode block as described in claim 11 in which the dimensions of said resonant cavities and said strapping rings are related according to the equation:

cos 2lcl-cos Ln N Us 1 0 9w Leos sin klcos kl sin kl where P=1z+111N 112:0, i1, i2, i3,

N=number of cavities x/s /a =admittance of free space w angular frequency at which the device is to be operated c=velocity of light in free space 9 Y =equivalent characteristic admittance of each pair of conductive strapping members as a two wire transmission line l=average length of strap per cavity n =radius of the anode 5 r =radius of the cathode 19=angle at which walls of cavity would intersect a=distance from point where walls of cavity would intersect to front of cavity b distance from point where walls of cavity would inter- 10 sect to back of cavity 17. A cavity resonator magnetron anode block as described in claim 14 in which the dimensions of said resonant cavities and said strapping rings are related according to the equation: 15

yn+yr+ s= Where I y =the admittance of the interaction space of the magnetron 20 y =the admittance of the cavity y =the admittance of the strapping ring said admittances being defined by the following equations:

cos 2lcZ-cos 42E N ZIS J 7m cos sin kl-cos kl sin kl N T a 5) 19 where P=n+mN m= 0', i1, i2, i3, N =number of cavities n=O, l, 2, N/Z J'=\/ /e =admittance of free space k=w/C w=angular frequency at which the device is to be operated c=velocity of light in free space Y =equivalent characteristic admittance of each pair of conductive strapping members as a two wire transmission line l=average length of strap per cavity r =radius of the anode r radius of the cathode 0=angle at which walls of cavity would intersect a=distance front point where walls of cavity would intersect to front of cavity b=distance from point where walls of cavity would intersect to back of cavity References Cited in the file of this patent UNITED STATES PATENTS 2,496,500 Spencer Feb. 7, 1950 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 121,821 February 18, 1964 Se Puan Yu It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 3, lines 40 and 41, and column 10, lines 17 and 18, the equations, both occurrences, should appear as shown below instead of as in the patent? column 4, line 51, for "elemnts'F'j read elements column 5-, line 20, for "on" read one column 7, line 23, for "coperating" read cooperating v Signed and sealed this 14th day of July 19 64.

(SEAL) Attest:

E'STON- G. J-CHNSON EDWARD" J. BRENNER Attesting Officer Commissioner of Patents 

7. IN A CAVITY RESONATOR MAGNETRON, A CIRCULAR ANODE BLOCK HAVING A PLURALITY OF RESONANT CAVITIES BEING EQUALLY SPACED FROM EACH OTHER IN SAID BLOCK, SAID CAVITIES BEING OF AT LEAST THREE DIFFERENT SIZES, A PLURALITY OF SEGMENTS, ONE EACH OF SAID SEGMENTS SEPARATING ADJACENT ONES OF SAID CAVITIES, SAID CAVITIES OF DIFFERENT SIZES BEING RANDOMLY DISPOSED IN SAID BLOCK, AND STRAPPING MEANS COMPRISING AT LEAST TWO ANNULAR CONDUCTIVE MEMBERS, SAID MEMBERS ALTERNATELY CONTACTING ADJACENT ONES OF SAID SEGMENTS, EACH OF SAID MEMBERS HAVING A PLURALITY OF SECTIONS COOPERATING WITH RESPECTIVE DIFFERENT INDIVIDUAL ONES OF SAID CAVITIES, SAID SECTIONS BEING OF AT LEAST THREE DIFFERENT SIZES WHEREBY EACH ONE OF SAID CAVITIES AND THE SECTIONS OF SAID MEMBERS COOPERATING THEREWITH PRESENT A SUBSTANTIALLY UNIFORM IMPEDANCE TO AN ELECTROMAGNETIC WAVE OF A PREDETERMINED FREQUENCY. 